What is the Serial Console

The serial console is allowing to get message output from the boot process. You can check the boot log (you can even interrupt it to enter some commands), and also the kernel boot log.
It's mainly usefull when developping some boot or kernel modifications, this way, if something goes wrong at the startup (aka kernel panic), you'll be able to see where it stopped.

How to get a serial console log on the TsP

Many Bufalo's devices need some soldering work to get the console output over the serial link, the good news with the TeraStation Pro is that you don't even need to open the box to get serial console access because you can use the UPS serial port ! The "bad" news is that you need to start the TsP at least one time to switch the serial link from UPS function to serial function.
There are 2 methods to switch the serial link to console mode :

Once the switching is done, you can reboot your TsP (A power-off will reset the serial switchin to UPS function, a rebbot will keep the setting as defined by the user). You'll then be able to see console output using HyperTerminal application.
The serial port configuration is the following :

57600bps, 8bit, 1 stop bit, no parity, no flow control

You'll also need to connect your computer to the TsP using a cross over serial cable.